Search: support when javascript is disabled

Unclear how important this is.

[A 2010 study by Yahoo](https://web.archive.org/web/20120118011844/http://developer.yahoo.com/blogs/ydn/posts/2010/10/how-many-users-have-javascript-disabled/) seems to have the best data and found a 2% rate of JS being disabled in the US, but other countries was much lower.

[This newer study](https://blockmetry.com/blog/javascript-disabled) had it closer to 0.2% in 2016 across all devices.

[A large percentage of the users](https://gds.blog.gov.uk/2013/10/21/how-many-people-are-missing-out-on-javascript-enhancement/) (0.9% out of 1.1% total) who are blocked are also getting blocked by corporate firewalls rather than because the end user actually disabled JS.

I suspect that we should just detect when js is failing and display a message and/or a link that lets the user fallback to our existing search API in some way. But that also means we need to support that existing code going forward.

Start by reviewing the existing search API referenced in the issue and the current JavaScript-driven search flow. Determine how JavaScript failure could be detected and define a fallback or message, with completion requiring a decided scope and support for the existing API going forward.

Written by the indexing model from the issue text.